I want to create a dataframe containing the possible permutations of a set of items, where each item can either be included or not.

I was thinking that the finished dataframe ought to look something like:

```
| group | item | included |
|-------|------|----------|
| 1 | a | T |
| 1 | b | F |
| 1 | c | F |
| ... | ... | ... |
```

Therefore we would have 2^n unique groups (including the one where all items are not included).

My initial thought was to use `tidyr::crossing`

to create the different combinations; however, since it does not supply a group identifier on the resulting dataframe, I have been struggling.

```
suppressPackageStartupMessages(library(tidyverse))
n_items <- 5
items <- letters[1:n_items]
n_included <- 1:n_items
generate_split <- function(x, len) {
tibble(split = x,
included = c(rep(TRUE, x), rep(FALSE, len - x)),
row = 1:len)
}
map(n_included, generate_split, len = n_items) %>%
map(~ crossing(.x, item = items))
#> [[1]]
#> # A tibble: 25 x 4
#> split included row item
#> <int> <lgl> <int> <chr>
#> 1 1 TRUE 1 a
#> 2 1 TRUE 1 b
#> 3 1 TRUE 1 c
#> 4 1 TRUE 1 d
#> 5 1 TRUE 1 e
#> 6 1 FALSE 2 a
#> 7 1 FALSE 2 b
#> 8 1 FALSE 2 c
#> 9 1 FALSE 2 d
#> 10 1 FALSE 2 e
#> # ... with 15 more rows
#> # ... (rest of the list items)
```

Any help in reaching the solution would be greatly appreciated.